The present invention relates to a thin film deposition system and, more particularly, to a thin film deposition system having an electrode construction suited to apply radio frequency bias voltage to a substrate in an inline or load lock type system for mass-production.
Thin film deposition systems by sputtering are used widely in various fields as important means for deposition of thin films or layers of various kinds of material. In particular, nowadays, miniaturization and enhancement in performance are progressing, and mass-production by the sputtering system is required. In order to satisfy the requirement, various techniques has been developed. Particularly, bias sputtering technique and an inline film deposition technique each have become important among those techniques.
The bias sputtering employing radio frequency, which is different in mechanism from etching, effects sputtering and film deposition at the same time, so that it is difficult to incorporate the bias sputtering into an inline system. Therefore, most of conventional thin film deposition system bias sputtering are such a type that a substrate on which a thin film is to be deposited is fixed, as disclosed in Japanese Patent Laid-Open No. 62-253765 (1987). As a special case, Japanese Patent Laid-Open No. 62-80266 (1987) discloses a thin film deposition system provided with a carrousel type rotational substrate holder to which bias is applied. However, an inline type thin film deposition system of a substrate transfer type, which can be used as an inline system, has not been put into practice as yet.
In case of effecting bias-sputtering by radio frequency in an inline sputtering system, radio frequency bias voltage control, radio frequency plasma control, etc. are important subjects. The condition that radio frequency is applied to a movement type substrate holder influences greatly the film deposition.
Namely, an electrode for applying radio frequency to the substrate holder holding a substrate is connected to or disconnected from the substrate holder at each time the substrate is transferred. The contact condition between the substrate holder and the electrode changes greatly a reactance component of impedance of a electrode circuit. Therefore, even if negative bias voltage is monitored at a radio frequency power source side, it is difficult to suitably control the electric power to be supplied to the substrate holder, therefore, change in film deposited on the substrate is inevitable. Even if the bias power is constant, change in the bias voltage, even change of 20 to 30%, often takes place in order to make the bias voltage constant.
On the other hand, a weak glow-discharge is generated between the substrate or substrate holder and the vacuum chamber wall when radio frequency power is applied on the substrate. Although this is because of no provision of a suitable shield for shielding radio frequency, it is very difficult to provide the shield so as to cover completely the substrate holder which is constructed to be movable. Therefore, power loss is inevitable. Further, when the reactance component of the RF (radio frequency) shield to the electrode is not made exactly the same at each time of transfer of the substrate, stable film deposition can not be achieved.
Further, if the substrate or the substrate holder is provided with the RF shield, it is troublesome to provide a heater for heating the substrate. In case the RF shield is provided, it is necessary to be keep a very narrow gap of about 2 to 4 mm between the shield and the substrate holder in order to suppress the formation of discharge between the shield and the substrate or the substrate holder. Therefore, it is difficult to provide the heater in such a narrow gap.